docs: def get_otp(hsm, args):
      """ Get OTP from YubiKey. """
      if args.no_otp:
          return None
      if hsm.version.have_unlock():
          if args.stdin:
              otp = sys.stdin.readline()
              while otp and otp[-1] == '\n':
                  otp = otp[:-1]
          else:
              otp = raw_input('Enter admin YubiKey OTP (press enter to skip) : ')
          if len(otp) == 44:
              # YubiHSM admin OTP's always have a public_id length of 6 bytes
              return otp
          if otp:
              sys.stderr.write("ERROR: Invalid YubiKey OTP\n")
      return None